Electron tube grids



Jan. 3, 1956 E. COHN 2,729,763

ELECTRON TUBE cams Filed March 19, 1952 GRIDS OF RHODIUM NICKEL ALLOYINVENTOR Z'zqgene 00/122 BY I I TTW Patent Office 2,729,763 PatentedJan. 3, 1956 2,729,763 ELECTRON Eugene Cohn, Whitejl'laiiss, N.Application March 19, 1952,Serial'No. 277,403 .1 Claim. (or. 313 311This invention relates to electron tubes, and more particularly tominiature and subminiature electron tubes 'having one or more gridstherein. By a miniature electrons tube is meant an electron tube,theenvelope of which has a height not exceeding approximately 1 /2inches and an outside diameter not exceeding about 4 inch, and by asubminiature electron tube is meant an electron tube the envelope ofwhich has a height not exceeding about 1% inches and an outside diameternot exceedingab ut in h- In the manufacture of miniature andsubminiature electron tubes successive convolutions of the gridsemployed therein are usually spaced apart minute distances. Also .thedistance between the grids'or between the innermost grid and the cathodeis verysmall. Such close spacing, in operation of the tube, to meetcommercial specifications must be maintained within a tolerance of theorder of only .0005 .inch. The grid wire must have adequatetensilestrength to permit winding underthe nece ary ension to maintain sch. p g within. th o e ances above noted dur n cleaning sizing and, othr h l to hi h. th grids e jecte in the. manufacture of the tube. Alsothe grid wire must have the necessary physical characteristics to remainin the desired spaced relationship relative to successive convolutionsof the grid and to the other parts of the tube during operation of thetube at the elevated temperatures which then occur due, for example, toheating of the cathode. The grid wire must also have the property of notdeveloping harmful oxides when the grid is made and also duringsubsequent heat treatment employed in making the tube, for example, toeffect its exhausting. In use, the grid should not emit electrons insuflicient quantities to deleteriously affect the operation of theelectron tube; this phenomena is commonly known as and will behereinafter referred to as secondary emission.

In the manufacture of electron tubes, and particularly the miniature andsubminiature electron tubes, it is now conventional practice to producethe grid from tungsten wire coated with a precious metal, such as gold,palladium, rhodium or platinum, usually gold. The precious metal coatingis employed to minimize the formation of harmful oxides and to reducesecondary emission; the tungsten base is employed to obtain thenecessary tensile strength. Such grids have been found objectionable fora number of reasons among which may be mentioned it is frequentlynecessary to operate the cathode at such high temperatures thatvaporization of the plated gold takes place with consequent impairmentof the operation of the tube. Furthermore, the tungsten grid Wire ofnecessity must be made by a powder metallurgy technique. This results ina wire that is not uniform throughout its length, i. e., the wire hasbrittle or weak spots along its length. Such variations in the wirecause difiiculties when the wire is wound to form a grid; for example,brittle spots in the wire may deleteriously affect the aforesaid spacingor result in the wire breaking as it is wound to form the grid.

It is an object of this invention to provide an electron tube having oneor more grids therein, which in use show no harmful secondary emission,conform with existing tolerances, can be operated without harmfuleffects at materially higher temperatures than heretofore known gridsincluding the commonly used g'oldplated tungsten grid, and do notdevelop harmful oxides during fabrication of the electron tube or in usethereof. 1

.Other objects and advantages ofthis invention will be apparent from thefollowing detailed description thereof.

In accordance with this invention the grid or grids of theelectron tubesaremade by'windi'n'g a wire-consisting of analloy containing from 30% to50% rhodium, from 44% to 70% nickel and from 0% to-6% molybdenumortungsten, the wire having a diameter of from .00l5 .0004 inch undertension about the gridsupports to produce the grid winding. The alloy isproduced by melting the rhodium,- nickel and molybdenum ortugnsten, ifemployed, in the proportions within the ranges above noted, producing aningot from the melt, then wire drawing and annealing between successivewire drawing operations to produce 'a *giid wire of the desireddiameter. As the production of the wire may be in 'accordance with anywell known procedure for producing fine wire of maximum tensilestrength, it is believed further description thereof would serve nouseful purpose.

The nickel constituent of the alloy may be pure nickel or the commercialgrade of nickel sold byInternational Nickel Company as Grade A nickelwhich contains 99.4% nickel and cobalt, the rest being impurities foundin commercial nickel. The rhodium, tungsten and molybdenum -may be pureor commercial--grads containing trace amounts of impurities. Preferredalloys are: a

(a) 43% rhodium and 5.7% nickel;

(b) 42.2% rhodium, 53.9% nickel and 3.9% molybdenum;

(c) 42.2% rhodium, 53.9% nickel and 3.9% tungsten.

Melting of the rhodium, nickel and molybdenum or tungsten, if used, toproduce an alloy ingot which is wire drawn to a diameter size of from.0015 to .0004 inch and annealing between successive wire drawingoperations results in a wire having a surprisingly high tensilestrength, e. g., over 300,000 pounds per square inch and usually about360,000 pounds per square inch in the case of a wire having a diameterof .001 inch.

The accompanying drawing shows, for purposes of illustration only, anelectron tube of the pentode type. In this drawing Figure 1 is aperspective view on an enlarged scale showing a conventional type ofelectron tube in which the invention may be embodied, the glass envelopebeing broken away to show the interior structure of the tube;

Figure 2 is a fragmentary perspective view on a still larger scaleshowing the relative arrangement of the grids, cathode and plate; and

Figure 3 is a horizontal section taken in a plane passing through line3-3 of Figure 2.

Referring to the drawing, 10 indicates a glass bulb or envelope whichencloses the five electrodes of the tube. The electrode assembly ismounted in the usual Way on the base 11 which carries a heated cathode12, a control grid 13, a screen grid 14, a suppresser grid 15 and aplate 16 all surrounding the cathode 12. Suitable spacers 17 and 18space the electrodes from each other and prevent lateral displacement ofthe assembly in the tube.

Spaced rods 19 and 20 are suitably supported at their ends in thespacers 17 and 18 and provide supports for the successive convolutionsof the grid wire wound thereabout to form the control grid 13. This wireis wound under tension sufficient to maintain successive convolutions ofthe wire in desired spaced relation and also to maintain the desiredspacing between the control grid 13 and the cathode 12 and between thecontrol and screen grids. Similarly, spaced rods 21 and 22 providesupports for the convolutions of the grid wire forming the screen gridand supports 23 and 24 to provide supports for the convolutions of thegrid wire forming the suppresser grid. Some or all of these supportingrods may be provided with spaced niches or serrations for receiving andholding the wire wound thereabout, as is well known in this art.

Leads 25 extend from the plate, grids and cathode as is conventional.Since the construction of the electron tube apart from the compositionof the grid wire may be of any well known type, it is believed furtherdescription thereof is unnecessary.

In accordance with this invention the control and screen grids and, ifdesired, also the suppresser grid are made by winding the rhodium nickelalloy hereinabove described about the grid supports under tensionsufficient to maintain the grid wire in place on the grid supports. Thetension used will depend on the structure of the grid supports, thedesign of the tube, etc. In view of the high tensile strength of therhodium nickel alloys, the grid wire can readily be wound about itssupports under tension as high as 300,000 pounds per square inch withoutdanger of the wire breaking and the wound wire will remain in thedesired spaced relationship on the grid supports.

In use it has been found that grids made of the rhodium nickel alloysherein disclosed do not develop harmful secondary emission or oxides.Further, the grid wire has the necessary strength and other physicalproperties to maintain the aforesaid spacing within the tolerance abovenoted during the handling of the grids necessary in order to mount thegrids within the vacuum tubes and also in use of the tubes, even at therelatively high temperatures at which the cathode may be operated. Sincethe grid wire is produced from an alloy melt and not by a metallurgicaltechnique, it is uniform in its physical properties and chemicalcomposition throughout its length. Because of this greater uniformity itcan be wound with less danger of breaking and will maintain theaforesaid spacing within the tolerance above noted much more effectivelythan the gold plated tungsten wire heretofore used.

While I have described my improvement in connection with the grid of aminiature or subminiature electron tube, it will be understood theinvention is applicable to the production of grids of other electrontubes.

Ordinary commercial rhodium and nickel often contain traces of othermetals, such as platinum and silver. Hence, the presence of tracequantities of such other metals in the alloy is not to be construed as adeparture from the scope and spirit of the invention.

Since different embodiments of the invention could be made withoutdeparting from the scope of this invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawing shall be interpreted as illustrative and not in a limitingsense.

Having thus described my invention, what I 'claim as new and desire tosecure by Letters Patent is:

A grid electrode suitable for use in an electron tube consisting of analloy wire having a diameter from .0015 to .0004 inch, the alloyconsisting of from 30% to'50% rhodium, from 44% to nickel and from 0% to6% of a metal from the group consisting of tungsten and molybdenum.

References Cited in the file of this patent UNITED STATES PATENTS1,169,182 Nicolson Jan. 25, 1916 1,779,602 Kingsbury Oct. 28, 19301,832,307 Kingsbury Nov. 17, 1931 1,975,140 Eitel et al. Oct. 2, 19342,015,327 Wheeler Sept. 24, 1935 2,066,870 Wise et al. Jan. 5, 19372,081,125 Carter a- May 18, 1937 2,472,760 Ratchford June 7, 19492,533,750 Adler et a1 Dec. 12, 1950 2,567,714 Kaplan Sept. 11, 1951

